Manufacturing & Prototyping

Freeze Tape Casting of Functionally Graded Porous Ceramics

Pore structures can be tailored in ways heretofore impossible. Freeze tape casting is a means of making preforms of ceramic sheets that, upon subsequent completion of fabrication processing, can have anisotropic and/or functionally graded properties that notably include aligned and graded porosity. Freeze tape casting was developed to enable optimization of the microstructures of porous ceramic components for use as solid oxide electrodes in fuel cells: Through alignment and grading of pores, one can tailor surface areas and diffusion channels for flows of gas and liquid species involved in fuel-cell reactions. Freeze tape casting offers similar benefits for fabrication of optimally porous ceramics for use as catalysts, gas sensors, and filters.

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Electrophoretic Deposition on Porous Non-Conductors

EPD is simplified and made more widely applicable. A method of electrophoretic deposition (EPD) on substrates that are porous and electrically non-conductive has been invented. Heretofore, in order to perform an EPD, it has been necessary to either (1) use a substrate material that is inherently electrically conductive or (2) subject a non-conductive substrate to a thermal and/or chemical treatment to render it conductive.

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Rapid and Quiet Drill

This is an all-ultrasonic variant of previously reported ultrasonic/sonic drills. The figure depicts selected aspects of the rapid and quiet drill (RAQD), which is a prototype apparatus for drilling concrete or bricks. The design and basic principle of operation of the RAQD overlap, in several respects, with those of ultrasonic/sonic drilling and coring apparatuses described in a number of previous NASA Tech Briefs articles. The main difference is that whereas the actuation scheme of the prior apparatuses is partly ultrasonic and partly sonic, the actuation scheme of the RAQD is purely ultrasonic. Hence, even though the RAQD generates considerable sound, it is characterized as quiet because most or all of the sound is above the frequency range of human hearing.

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Hydrogen Peroxide Concentrator

Water is removed through selectively permeable membranes. A relatively simple and economical process and apparatus for concentrating hydrogen peroxide from aqueous solution at the point of use have been invented. The need for this or a similar invention arises for the following reasons:

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Process for High-Rate Fabrication of Alumina Nanotemplates

Approximately regular hexagonal arrays of holes are formed in an anodizing process. An anodizing process, at an early stage of development at the time of reporting the information for this article, has shown promise as a means of fabricating alumina nanotemplates integrated with silicon wafers. Alumina nanotemplates are basically layers of alumina, typically several microns thick, in which are formed approximately regular hexagonal arrays of holes having typical diameters of the order of 10 to 100 nm. Interest in alumina nanotemplates has grown in recent years because they have been found to be useful as templates in the fabrication of nanoscale magnetic, electronic, optoelectronic, and other devices. The present anodizing process is attractive for the fabrication of alumina nanotemplates integrated with silicon wafers in two respects: (1) the process involves self-ordering of the holes; that is, the holes as formed by the process are spontaneously arranged in approximately regular hexagonal arrays; and (2) the rates of growth (that is, elongation) of the holes are high enough to make the process compatible with other processes used in the mass production of integrated circuits.

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Fluorine-Based DRIE of Fused Silica

A suitable choice of process parameters enables etching of vertical side walls. A process of deep reactive-ion etching (DRIE) using a fluorine-based gas mixture enhanced by induction-coupled plasma (ICP) has been demonstrated to be effective in forming high-aspect-ratio three-dimensional patterns in fused silica. The patterns are defined in part by an etch mask in the form of a thick, highquality aluminum film. The process was developed to satisfy a need to fabricate high-aspect-ratio fused-silica resonators for vibratory microgyroscopes, and could be used to satisfy similar requirements for fabricating other fused-silica components.

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Mechanical Alloying for Making Thermoelectric Compounds

Constituents are ball-milled into a powder, which is then hot pressed. An economical room-temperature mechanical alloying process has been shown to be an effective means of making a homogeneous powder that can be hot-pressed to synthesize a thermoelectric material having reproducible chemical composition. The thermoelectric materials to which the technique has thus far been applied with success include rare-earth chalcogenides [La3–xTe4 (0 < x < 0.33) and La3–xYbyTe4 (0 < x < 1, 0 < y < 1)] and Zintl compounds (including Yb14MnSb11 and Yb14BiSb11). The synthesis of a given material consists of the room-temperature thermomechanical- alloying process followed by a hot-pressing process. Relative to synthesis of nominally the same material by a traditional process that includes hot melting, this synthesis is simpler and yields a material having superior thermoelectric properties.

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